This invention relates to sedimentation apparatus. More specifically, this invention relates to a system for removing surface scum from a liquid treatment tank such as a sewage clarification tank.
In sewage treatment plants, waste is fed to clarification tanks. Denser solids in the sewage settle to the bottoms of the tanks. In the course of treatment, a layers of lighter solids accumulates on the top of a substantially liquid body undergoing treatment. This layer of scum varies in composition and thickness.
Present scum removal systems have inherent problems regarding maintenance and efficiency. Associated factors include varying liquid levels in the tanks, ice build up in cold climates, and extreme variations in the density and depth of the surface film.
In one prior kind of scum removal system, a wiper or skimmer is moved across the surface of the liquid to push the floating materials towards a scum trough which guides the scum away from the clarification tank. The skimmer may take the form of a floating boom, such as disclosed in U.S. Pat. No. 4,054,520 to McGivern. In the scum removal system of that patent, the floating skimmer boom is urged across the surface of the liquid by a carriage towards a floating beach fixed to an upper edge of the scum trough. A roller mounted to the carriage assembly and disposed forwardly of the skimmer boom engages a leading portion of the floating beach and forces the beach downwardly, thereby permitting the scum layer which is caught between the skimmer boom and the beach to wash over the beach into the scum trough. Upon reaching the end of its cleaning stroke, the skimmer boom is pushed up a ramp onto a saddle on the carriage, where the skimmer boom remains until the carriage has returned to a starting position. With a retreat of the carriage away from the scum trough, the beach is freed to resume its upper position, blocking entry of further liquid and surface scum into the scum trough. Upon the return of carriage to its starting position, which is spaced from the scum trough, the skimmer boom is pushed from the saddle back onto the liquid surface for another approach towards the beach.